China blanketed Tiananmen Square with police officers Thursday, determined to prevent any commemoration of the 20th anniversary of a military crackdown on pro-democracy protesters that left hundreds dead.

Visitors to the sprawling plaza in central Beijing were stopped at checkpoints and searched, and foreign television crews and photographers firmly turned away. Uniformed and plainclothes officers, easily identifiable by their similar shirts, seemingly outnumbered tourists.

A few pursued television cameramen with opened umbrellas trying to block their shots — a comical dance that was broadcast on CNN and BBC.